Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.
It can feel confusing when the number on the scale goes up, even when you’re doing all the right things. You’re eating well, moving more, and maybe even feeling stronger, but your weight seems to creep up instead of down.
Before you panic or throw in the towel, there’s something important to consider: not all weight gain is fat. An increase in muscle mass can raise your body weight while actually improving your health. A study shows that as lean body mass increases, even alongside a higher BMI, it’s linked to better metabolic outcomes and a lower risk of conditions like metabolic syndrome.
In this blog, we’ll walk through the signs that your body is changing in a positive way, even if the scales don’t show it just yet.
Muscle gain happens when your body repairs and builds stronger muscle fibres in response to resistance or strength training. When you lift weights, do bodyweight exercises, or perform any activity that challenges your muscles, tiny tears form in the muscle tissue. Your body responds by repairing those fibres, and in the process, making them thicker and stronger.
This process is known as muscle hypertrophy, and it doesn’t happen overnight. It requires consistency, adequate nutrition (especially protein), and enough rest. Over time, as your muscle mass increases, it can shift your body composition, although the number on the scale stays the same or increases slightly.
Not all progress shows up on the scale. If you’ve been working out consistently and eating well, these signs can help you identify whether your recent weight gain is actually muscle, not fat.
One of the first visual signs of muscle gain is improved definition. You may notice your arms, legs, or core starting to look more toned, even if the scale hasn’t budged. Over time, your body might take on a more sculpted, athletic appearance, like broader shoulders, firmer muscles, and more visible shape in the areas you’ve been targeting.
Unlike fat, which softens the body’s contours, muscle adds structure and tone. These changes may be gradual, but they’re a good indicator that your training is paying off. And it’s not just what you lift, but how you lift it. A study indicates that spending more time under tension during each rep can significantly boost muscle-building activity. This helps enhance that firm, sculpted appearance many people associate with muscle gain.
Steady strength improvements are a reliable sign that you’re building muscle. If you're lifting heavier weights, doing more reps, or pushing through workouts that once felt tough, your muscles are clearly adapting and growing stronger. This is backed by research showing that progressive overload, which means gradually increasing the weight or reps over time, is essential for muscle growth and strength gains. Improvements in strength reflect both neural adaptations (your nervous system getting more efficient) and actual increases in muscle fibre size.
Even small gains, like improving your form or increasing resistance in bodyweight exercises, show that your strength and muscle capacity are on the rise.
Muscle gain often shows up in how your clothes fit and how your body measures, especially in targeted areas like the arms, thighs, and chest. If your shirts are tighter across the shoulders or your jeans feel snug around the legs, it could reflect muscle development rather than fat gain.
You might also notice specific measurements going up while your waistline remains stable or shrinks. These shifts in shape and fit are often more telling than the number on the scale.
Research using ultrasound to measure muscle changes found that even when traditional body measurements didn’t change, meaningful increases in muscle thickness, particularly in the quadriceps, were still detected. This supports the idea that localised muscle gains can alter your body’s shape and the way clothes fit, even if those changes aren’t obvious on the scale or with a tape measure.
As your muscle mass increases, your body becomes more efficient at using energy, both during exercise and in everyday tasks. This often translates to feeling more energised throughout the day, with less effort required for things that used to tire you out.
According to a study, the efficiency of muscular work can also improve with practice and training due to better coordination, meaning your body uses less energy to perform the same tasks. As both muscle mass and neuromuscular control improve, you'll likely experience more energy and less fatigue throughout the day.
If you’re noticing improved stamina, better focus, and fewer afternoon crashes, it could be a sign that your body is adapting to increased physical activity by building muscle. Importantly, this type of energy boost tends to come without the heaviness or sluggishness that can accompany fat gain.
Building on that improved energy efficiency, you may also find that everyday tasks feel less physically demanding. Carrying groceries, climbing stairs, or lifting objects becomes noticeably easier as your strength increases.
You might also notice that your workouts are smoother: movements feel more controlled, your form is better, and you’re able to get more out of each session. These changes show that your body is adapting to your training and becoming more capable and coordinated.
As your muscles adapt and grow stronger, your body becomes more efficient at repairing tissue after workouts. You may find that post-exercise soreness doesn’t last as long, or that you bounce back more quickly between training sessions. Research supports this: in a study where participants repeated a high-intensity eccentric exercise, their muscles showed less damage and faster recovery the second time around, even when the workout was just as demanding.
Shorter recovery times are a sign that your muscles are not only growing, but also becoming more resilient. It means your body is handling the physical stress of training better—a strong indication that your fitness level is improving and muscle mass is increasing.
If the number on the scale is increasing but your waist measurement remains the same, or is even shrinking, it’s a strong indicator that you’re gaining muscle, not fat. Muscle gain often shows up in areas like the arms, chest, and legs, while fat gain typically accumulates around the midsection.
Tracking your waistline alongside your weight can give you a clearer picture of what’s really changing. A stable or smaller waist, despite a higher weight, suggests an improvement in body composition rather than unwanted fat gain.
When you're building muscle, you’ll often notice your body feeling firmer to the touch, especially in areas you’ve been actively training. This is a key difference between muscle and fat: muscle has a denser, more solid feel, while fat tends to be softer and less structured.
If your arms, legs, or core feel more toned and supportive, even when relaxed, it’s a sign that lean muscle is developing. These physical changes may not always be visible at first, but the firmer feel is a reliable indicator of muscle growth beneath the surface.
If the number on the scale has been puzzling you lately, remember that weight alone doesn’t tell the full story. Building muscle can shift your shape, boost your strength, improve your energy levels, and contribute to better health, even if your weight increases.
Look for signs in how you feel, perform, and fit into your clothes rather than relying solely on the scales. These subtle changes can be some of the clearest indicators that you’re making meaningful progress. Muscle gain takes time and consistency, but the long-term benefits to your health and body composition are well worth it.
Want confirmation you're gaining muscle, not just losing fat? Explore Signs You're Losing Fat, Not Muscle. This article breaks down clear signs like maintained strength, toning, and energy that show you're building lean muscle while dropping fat.
Dr Nick Fuller is the founder of Interval Weight Loss and is a leading obesity expert at the University of Sydney with a Ph.D. in Obesity Treatment. Dr Fuller is also the author of three best-selling books and his work been published in top ranked journals in the medical field, including JAMA, Lancet and American Journal of Clinical Nutrition.